#include <sys/types.h>
#include <sys/msg.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void msg_stat(int,struct msqid_ds );
int main()
{
int gflags,sflags,rflags;
key_t key;
int msgid;
int reval;
struct msgsbuf{
        int mtype;
        char mtext[1];
    }msg_sbuf;
struct msgmbuf
    {
    int mtype;
    char mtext[10];
    }msg_rbuf;
struct msqid_ds msg_ginfo,msg_sinfo;
char* msgpath="/unix/msgqueue";
key=ftok(msgpath,'a');
gflags=IPC_CREAT|IPC_EXCL;
msgid=msgget(key,gflags|00666);
if(msgid==-1)
{
    printf("msg create error\n");
    return 0;
}
//创建一个消息队列后，输出消息队列缺省属性
msg_stat(msgid,msg_ginfo);
sflags=IPC_NOWAIT;
msg_sbuf.mtype=10;
msg_sbuf.mtext[0]='a';
reval=msgsnd(msgid,&msg_sbuf,sizeof(msg_sbuf.mtext),sflags);
if(reval==-1)
{
    printf("message send error\n");
}
//发送一个消息后，输出消息队列属性
msg_stat(msgid,msg_ginfo);
rflags=IPC_NOWAIT|MSG_NOERROR;
reval=msgrcv(msgid,&msg_rbuf,4,10,rflags);
if(reval==-1)
    printf("read msg error\n");
else
    printf("read from msg queue %d bytes\n",reval);
//从消息队列中读出消息后，输出消息队列属性
msg_stat(msgid,msg_ginfo);
msg_sinfo.msg_perm.uid=8;//just a try
msg_sinfo.msg_perm.gid=8;//
msg_sinfo.msg_qbytes=16388;
//此处验证超级用户可以更改消息队列的缺省msg_qbytes
//注意这里设置的值大于缺省值
reval=msgctl(msgid,IPC_SET,&msg_sinfo);
if(reval==-1)
{
    printf("msg set info error\n");
    return 0;
}
msg_stat(msgid,msg_ginfo);
//验证设置消息队列属性
reval=msgctl(msgid,IPC_RMID,NULL);//删除消息队列
if(reval==-1)
{
    printf("unlink msg queue error\n");
    return 0;
}
}
void msg_stat(int msgid,struct msqid_ds msg_info)
{
int reval;
sleep(1);//只是为了后面输出时间的方便
reval=msgctl(msgid,IPC_STAT,&msg_info);
if(reval==-1)
{
    printf("get msg info error\n");
    return 0;
}
printf("\n");
printf("current number of bytes on queue is %d\n",msg_info.msg_cbytes);
printf("number of messages in queue is %d\n",msg_info.msg_qnum);
printf("max number of bytes on queue is %d\n",msg_info.msg_qbytes);
//每个消息队列的容量（字节数）都有限制MSGMNB，值的大小因系统而异。在创建新的消息队列时，//msg_qbytes的缺省值就是MSGMNB
printf("pid of last msgsnd is %d\n",msg_info.msg_lspid);
printf("pid of last msgrcv is %d\n",msg_info.msg_lrpid);
printf("last msgsnd time is %s", ctime(&(msg_info.msg_stime)));
printf("last msgrcv time is %s", ctime(&(msg_info.msg_rtime)));
printf("last change time is %s", ctime(&(msg_info.msg_ctime)));
printf("msg uid is %d\n",msg_info.msg_perm.uid);
printf("msg gid is %d\n",msg_info.msg_perm.gid);
}
